Getting ready for the move:
Rolly Brook gives all the details on applying for visas, moving your junk, and bringing all the right documents. He also kindly responds to emails.
For working and daily life questions:
I haunt the Mexico boards at Dave's ESL Cafe. They meander on about all sorts of delights, such as where to score olive oil, how to flake out of a teaching contract, and where to find the best airline deals.
For grumpy but ultimately helpful advice:
The retirees at MexConnect have kicked my ass more than once but at least I can outrun some of them...The discussion boards are meticulously detailed and address issues as diverse as medical insurance, monthly bills, favorite books about Mexico, and nailing the best exchange rate. The secret to all these discussion boards is the behind-the-scenes information you glean after posting a public message. Everyone starts PM-ing you with inside pointers, especially if they pity how poorly you're being treated on the forum. I've had to take my old advice I used to give my students and "rise above" a number of times.
For rose-colored-glasses swooning:
Well, I always find fiction can communicate more of the feeling of a place than guidebooks can and one of the better Mexico expatriate novels I've read is Harriet Doerr's Consider This, Senora.